Gas turbine systems are widely utilized in fields such as power generation. A conventional gas turbine system includes a compressor, a combustor, and a turbine. In a conventional gas turbine system, compressed air is provided from the compressor to the combustor. The air entering the combustor is mixed with fuel and combusted. Hot gases of combustion flow from the combustor to the turbine to drive the gas turbine system and generate power.
As requirements for gas turbine system emissions have become more stringent, one approach to meeting such requirements is to utilizing lean fuel and air mixtures in a fully premixed operations mode in the combustor to reduce emissions of, for example, NOx and CO. These combustors are known in the art as Dry Low NOx (DLN), Dry Low Emissions (DLE) or Lean Pre Mixed (LPM) combustion systems. These combustors typically include a plurality of primary nozzles which are ignited for low load and mid load operations of the combustor. During fully premixed operations, the primary nozzles supply fuel to feed a secondary flame. The primary nozzles typically surround a secondary nozzle that is utilized for mid load up to fully premixed mode operations of the combustor.
Secondary nozzles serve several functions in the combustor, including supplying fuel for the fully premixed mode, supplying fuel and air for a pilot flame supporting primary nozzle operation, and providing transfer fuel for utilization during changes between operation modes. In pilot mode, fuel for the operation of the pilot is directed through a pilot fuel passage typically located in the center of the fuel nozzle and air to mix with the pilot fuel is provided via a plurality of pilot air passages surrounding the pilot fuel passage. During transfer operation of the fuel nozzle, additional fuel is urged through the nozzle and into the combustion zone through a group of transfer passages located in the nozzle separate from the pilot fuel passage as a distinct flow of fuel. When the nozzle is not in transfer mode, the current practice is to purge the transfer passages of fuel by flowing transfer air through the transfer passages. In this operation the pilot is surrounded by this flow of lower temperature purge air. Separate passages in the secondary nozzle for pilot fuel, transfer fuel and air, and pilot air result in a complex nozzle assembly. Additionally, the pilot of the typical nozzle is fuel limited due to the configuration of the pilot fuel and air passages, so that high reactivity fuels cannot be utilized in the pilot.
Further, typical prior art secondary nozzles risk permanent damage due to flame-holding, when a flame is held in or adjacent to the nozzle. Because high reactivity fuels increase the risk of flame holding, the use of high reactivity fuels is thus further limited.
Thus, an improved secondary nozzle for a gas turbine system would be desired in the art. For example, a secondary nozzle that has a simple configuration and can perform several functions would be advantageous. Further, a secondary nozzle that resists permanent damage due to flame-holding would be advantageous.